Compact, light personal computers (also called "portable computers" or "notebook computers") built from designs that take portability considerations into account are in wide use today. Also, as compact auxiliary storage devices have been produced, certain notebook computers are now available that can incorporate a CD-ROM drive (CD replay device) in addition to a hard disk drive (HDD) and a floppy disk drive (FDD). As an example, the ThinkPad 755CD (an IBM Corp. trademark), a notebook computer that is sold by IBM Japan Ltd. incorporates a CD-ROM drive.
FIG. 1 shows an outline illustration of a notebook computer 1. The notebook computer 1 in FIG. 1 is so designed that a lid 5, which has an internally mounted liquid crystal display panel (LCD) 4, is rotatably hinged with a main body 3, almost at the rear edge of the main body 3. In the main body 3, which has a keyboard 2, are a CPU, a main memory, a ROM, peripheral controllers, and a system board on which is a bus by which these components (none of them shown) are connected. A battery pack (not show:n), an HDD (not shown), and a CD-ROM drive 50 are incorporated in the lower space of the main body 3 beneath the keyboard 2. A disk tray for the CD-ROM drive 50 is slideably mounted under the main body 3 to facilitate the exchange of disks. On the front face of the disk tray 51, an ejection (Eject) button 6 is provided to control the ejection of the tray. At its rear, the CD-ROM drive 50 is attachably connected to the bus on the system board (not shown) and can be removed and replaced by another peripheral device, such as an FDD.
The recording on a CD, i.e., a compact disk (hereafter also referred to simply as a "disk"), is performed by forming pits (which have raised and depressed shapes that differ in reflectivity) that correspond to digital data on one face of a disk, which is formed of a transparent resin, and by overlaying an extremely thin metal film of, for example, aluminum and a further hard protective film. The CD-ROM drive (CD replay device) focuses a laser beam on a rotating disk, and employs the changes in the intensity of reflected light to read data. Since a great amount of data can be recorded on a CD at high density, a CD is employed for the recording not only of computer data but also of audio data, image data and various other data.
The physical and logical specifications for a CD were determined by a group of which Sony Corporation and Philips Ltd. were the central figures, and are described in a "Reads Book," a "Yellow Book,". and a "Green Book," to use the common titles.
A CD is so designed that data are recorded spirally from the center of the disk surface to the outside and in the same density. The physical format is classified roughly into three areas: from the center of the disk face, a lead-in area, a program area, and a lead-out area. The lead-in and the lead-out areas are employed for recording attribute information for a disk and various control information concerning, for example, start positions for the individual tracks.
The program area is employed for recording the substantial user data, such as computer data and audio data, and is constituted by a single or a plurality of tracks. A track can be divided into frames that are 24 bytes long. The length of a track is not constant and varies depending on the length of the user data that are recorded. In case of a music CD, for example, one track corresponds to one piece of music, and the track length corresponds to the playing period.
A track on which computer data are recorded is called a "CD-ROM track," and a track on which audio track are recorded is called a "CD-DA track". In addition, as one type of a CD-DA, there is a "CD-Graphics" where image data are recorded in an empty area within the audio data (more specifically a sub channel in a frame). As another type, there is a hybrid CD having mixed CD-ROM tracks and CD-DA tracks. Also, as other standards, there are "CD-I (Compact Disk-Interactive media), where image data and audio data are recorded on a single track with an interleave factor (time- sharing multiplexing of a plurality of channels), and a "CD-ROM XA."
CD-DA specifications are given in a "Red Book," CD-ROM specifications are given in a "Yellow Book," and CD-I specifications are given in a "Green Book." The CD-I specifications prescribe the standards for enabling dialogue operation, and the CD-ROM XA specifications prescribe the standards for the combining of audio data with animated data and for their joint handling as multimedia.
Generally, in the same way as with other peripheral devices, a CD-ROM drive that is incorporated in a computer receives, through a bus, a command that is issued in software, such as an application program or an operating system (OS), so that it is controlled by a computer system (hereafter referred to simply as a "system"). The CD-ROM that replays a music CD is no exception. The starting and stopping of a read, and the head seek and set process for the next recorded musical piece will be discussed in detail.
To perform the reading of a music CD by an incorporated CDROM drive, it is assumed that at least three kinds of programs should be loaded into a main memory of the system: an application program for the music CD operation (hereafter referred, to as a "CD-PLAYER.EXE"), a file manager driver that permits an OS to manage a CD-ROM as an external storage device (MSCDEX. EXE, etc. ), and a device driver for a CD-ROM drive "CD-PLAYER.EXE" must be executed when a read operation is to be performed with a music CD. Since multitasking is not available with DOS environment, for example, the following procedures are required to run a music CD during the execution of another application (DOS word processing).
1. DOS word processing is temporarily terminated. (If a document is being prepared, it must be saved and the job is terminated.) PA0 2. A mouse program is activated if it has not yet been loaded. PA0 3. CD-PLAYER.EXE is executed. PA0 4. A pertinent selection (replay, halt, etc.) from a Graphical User Interface (GUI) screen menu is made by pointing and clicking with a mouse and the results of the operation are relayed to CD-PLAYER.EXE. PA0 5. CD-PLAYER.EXE is terminated. PA0 6. DOS word processing is resumed. PA0 1. The display for the Windows application that is being executed is minimized by a mouse operation, or a task is switched by depressing a toggle switch on a keyboard to provide a program manager window. 2. The icon of a program group wherein a CD-PLAYER icon is registered is opened. PA0 3. The CD-PLAYER icon is double-clicked to activate CD-PLAYER.EXE and a desired menu selection is clicked in the CD-PLAYER window. By referring to the above explanation, it would be understood by one having ordinary skill in the art that, conventionally, playing a music CD on a computer presents the following difficulties. PA0 (1) Interruption of an application that is being executed. PA0 (2) Use of system resources. PA0 (3) Operability.
Similarly, the following procedures are required to run a music CD during the execution of another application (Windows application) on Windows.
To control the starting or halting of replaying, a dedicated application, i.e., "CD PLAYER.EXE," must be activated every time. A bus is normally used to input data at a keyboard or with a mouse, and to transmit a command to a CD-ROM drive. Since an interrupt occurs at a CPU, an application that is being executed is inevitably suspended.
For frequent playing of music CDs, an application for operating a music CD (e.g., CD-PLAYER.EXE) and specific drivers, such as a file manager driver (e.g., MSCDEX.EXE) and a device driver, have to be resident in main memory. Since a CD-PLAY2R. EXE program is generally from 70 to 200 kilobytes, and since each of the drivers is about 35 kilobytes, together, these programs constitute a considerably large load on the system resources.
To play a music CD during the execution of another application, the application must be temporarily terminated and CD-PLAYER.EXE must be activated (in the DOS environment), or windows must be switched and the CD-PLAYER icon must be selected and operated (in the Windows environment). Also, the initiating operation is comparatively complicated. Since the user interface differs for each application, this is another factor that contributes to the complication and the difficulty of the operation.
In such an environment, even when a computer user becomes tired because of the work being done (e.g., the preparation of a document by word processing) and decides to listen to music to relax, the operation to replay a music CD requires the interruption of an application or the above described input operations. This is troublesome for a user.
Further, there are some applications (e.g., CD-PLAYER-EXE) that do not permit "working while listening to music"; and even if the replaying of a music CD can be performed, it is terminated when such application is ended. Even when an application can be terminated and the original application (e.g., word processing) can be restarted while a music CD is being replayed, the application must be activated each time for a succeeding music CD operation (the head seek-and-set process for playing the next recorded musical piece, or the playing ' halt), and further manipulation and time are required. It is clear that if several tens to several hundreds of kilobytes in a main memory are always used merely for audio data processing, not for computer data processing, system resources are wasted. In other words, although a user has installed a CD replay device in a computer system, such user cannot easily be refreshed by listening to music whenever desired.
On the other hand, since dedicated CD replay devices for playing music CDs are equipped, as a standard, with special control buttons for individual operations, such as replay start, replay halt, and the head seek-and-set process for the next musical piece, a user can replay music CDs freely, any time desired. As for an incorporated CD-ROM drive, however, generally, only the front face of a disk discharge tray appears on the surface of the computer main body 1, as is shown in FIG. 1. On such a limited surface, at most only an ejection button 6 is provided, and the addition of other control buttons increases manufacturing costs. Therefore, the operation of an incorporated CD-ROM drive relies on input that is performed at a keyboard or with a mouse. Accordingly, the operation of the CD-ROM drive requires the use of the bus and the interruption of an application program that is being executed.